1. Field of the Invention
This invention relates generally to the field of heating and specifically to minimizing leakage currents in a heating panel.
2. Description of the Related Art
Ovens are commonly heated by one or more of several means, including burning combustible gases and electrical resistance. One form of electrical resistance heating uses monolithic integrated heat sources, known as "heat panels," disposed on walls of the oven. Heat panels include a thermally and electrically conductive metal substrate or core covered by a thermally conductive and electrically insulative material on opposed faces. One face of the insulative material has a heating layer or film of electrically resistive material disposed thereon and connected to a current to generate heat. The heat is conducted through the other layers to the oven cavity. An example of such an apparatus is shown in U.S. Pat. No. 4,298,789 to Eichelberger, incorporated herein by reference.
Industry standards require the substrate to be connected to ground. The electrically conductive layers separated by an insulating layer form a capacitor. Thus, when an alternating current (AC) passes through the heating layer, a capacitive AC leakage current caused in the substrate and a resistive leakage current through the insulator become leakage current to ground when the substrate is connected to ground. The leakage current to ground will usually exceed industry standards or codes. Thus, the need exists for a heating panel type oven that will meet industry standards.
In addition, if the substrate is connected to neutral or ground of a power source, the leakage current should also be minimized. If the substrate is floating, the electrical potential that builds up on it must be as low as possible.